ATM signal processors

ABSTRACT

An ATM signal processor system for processing ATM data cells which in combination define a data package wherein the last cell of a package is characterized by an identifying code. The cells of different data packages are multiplexed to provide a serial data stream. A server and a buffer store via which the server is fed with the serial data stream are provided. The buffer store has a threshold capacity beyond which cells are discarded. A discarded cell identifier/rejecter serves to identify and store the identity of a data package with which a discarded cell is associated so as to be set thereafter to reject subsequently received cells with the same data package identity until being reset upon receipt of the last cell of the package as indicated by its characteristic identifying code.

BACKGROUND OF THE INVENTION

This invention relates to asynchronous transfer mode (ATM) signalprocessor systems and more especially it relates to such systems for ATMdata transmission wherein the transmission comprises a number of cellswhich are transmitted successively and which in combination define adata package or frame wherein the last cell of the package ischaracterized by an identifying data code.

When a plurality of transmissions are made each relating to a differentdata package, the cells of the various transmissions are multiplexed orinterleaved to provide a serial data stream. It will be appreciated thatATM data traffic is inherently bursty in nature, and in order toaccommodate widely varying data rates arriving at a server, a serialbuffer store is normally provided via which the server is fed with theserial data stream. Since in times of heavy traffic the capacity of thebuffer store may be inadequate, the buffer store is arranged to have anin-built threshold capacity beyond which data is discarded and lostwhereby re-transmission is required.

It will be appreciated that when a cell is discarded, the data packageof which it forms a part is corrupted such that subsequently transmittedcells which form part of the same data package are useless. As thebuffer store empties, however, useless subsequently received cellsrelating to the corrupted data package may nevertheless be stored in thebuffer so as to occupy buffer storage capacity which might be morefruitfully used. Thus, data transmission efficiency is reduced.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an ATM signalprocessor system wherein the cells of data packages corrupted asaforesaid are not needlessly stored, so that system efficiency isimproved.

According to the present invention, an ATM signal processor system isprovided for processing ATM data cells which in combination define adata package wherein the last cell of a package is characterized by anidentifying code. A means is provided for multiplexing the cells ofdifferent data packages to thereby provide a serial data stream. Aserver and a buffer store via which the server is fed with the serialdata stream is provided. The buffer store has a threshold capacitybeyond which cells are discarded. A discarded cell identifier/rejectermeans serves to identify and store the identity of a data package withwhich a discarded cell is associated, so as to be set thereafter toreject subsequently received cells with the same data package identityuntil being reset upon receipt of the last cell of the package asindicated by its characteristic identifying code.

The discarded cell identifier/rejecter may comprise address registermeans in which the address of discarded cells is stored and an inhibitormeans responsive to the address of subsequently received cells fordeleting them if their address corresponds to an address in theregister. An address is deleted from the register upon reception of acell having that address and additionally identified as a last cell in adata package; by its characteristic identifying code.

The address register means may comprise a mask register.

An embodiment of the invention will now be described by way of exampleonly with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an ATM signal processor systemaccording to the invention; and

FIG. 2 is a flow diagram for showing operation of the discarded cellidentifier/rejecter of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawing, cell streams relating data packages F1,F2, F3, and F4 are fed through a multiplexer 1 to provide a serial datastream 2. Each data package may comprise a number of cells, the finalcell only of which is identified as such by a characteristic code finalcell 3, as shown schematically in FIG. 1.

The multiplexed serial cell stream is fed to a buffer 4 including athreshold capacity 5 beyond which cells are discarded. The addresses ofdiscarded cells are stored by control of a discarded cellidentifier/rejecter 8 in a discard mask store register 6 which comprisesa plurality of mask address stores for storing addresses correspondingto a number of different cells. When the address of a discarded cell hasbeen stored, subsequently received cells are examined by theindentifier/rejecter and details of their address are fed over the lines7 to the discard mask store register 6. The discarded cellidentifier/rejecter 8 performs the following functions, as illustratedby the flow chart in FIG. 2. If correspondence results between theaddress of an incoming cell and an address stored therein, that incomingcell is deleted. In the event that a cell arrives having an addresswhich corresponds to one of the addresses stored in the register 6 andadditionally is identified by a characteristic code as a last cell 3 ofa data package, then the discard mask address store correspondingthereto is emptied so as to be available to receive the address of anewly discarded cell.

It will be appreciated that once a cell has been deleted due to bufferoverflow, when the threshold has been reached (which is the most commoncause of cell loss), the rest of the cells which form part of the sameframe or data package will also be deleted without increasing frameloss, whereby optimum use of the buffer store for desired cells isfacilitated. Thus, by deleting all cells making up a particular frame inconditions of high buffer usage, the continuing deletion of specificcells making up a frame, even after the buffer usage has dropped belowthreshold T, will reduce the chance of other frames being deleted.

Various modifications may be made to the arrangements shown withoutdeparting from the scope of the invention, and, for example, anysuitable address identifying/storage/discard means may be used, as willbe well known to those skilled in the art.

We claim as our invention:
 1. An Asynchronous Transfer Mode (ATM) signalprocessor system for processing ATM data cells which in combinationdefine data packages, and wherein a last cell of the data packages hasan identifying code, comprising:a multiplexer for multiplexing the cellsof different data packages to provide a serial data stream; a server; abuffer store via which the server is fed with said serial data stream,said buffer store having a threshold capacity beyond which cells arediscarded; a discard store register; and a discarded cellidentifier/rejecter for serving to identify and store in said discardstore register identity of a data package with which a discarded cell isassociated so that the identifier/rejecter thereafter rejectssubsequently received cells with the same data package identity untilthe discard store register is reset upon receipt of a last cell of saiddata package with which said discarded cell is associated as indicatedby its characteristic identifying code.
 2. A system according to claim 1wherein the discard store register stores addresses of discarded cells,and said discarded cell identifier/rejecter is responsive to addressesof subsequently received cells for deleting them if their addresscorresponds to an address in said discard store register, an addressbeing deleted from the discard store register upon reception of a cellhaving that address and additionally being identified as a last cell ina data package by its characteristic identifying code.
 3. A method forprocessing Asynchronous Transfer Mode (ATM) ATM data cells which incombination define data packages, and wherein a last cell of the datapackages has an identifying code, comprising the steps of:multiplexingthe cells of different data packages to provide a serial data stream;providing a server; feeding the serial data stream to a buffer store viawhich the server is fed with said serial data stream, said buffer storehaving a threshold capacity beyond which cells are discarded; providinga discard store register; and identifying and storing in the discardstore register identity of a data package with which a discarded cell isassociated, and thereafter rejecting subsequently received cells withthe same data package identity until the discard store register is resetupon receipt of a last cell of said data package with which saiddiscarded cell is associated as indicated by its characteristicidentifying code.